It is assumed that basic concepts of OPC UA information modelling, OPC Unified Architecture - Part 100, and OPC UA for Machinery - Part 1 are understood in this specification. This specification will use these concepts to describe the OPC UA for Compressed Air Systems Information Model. For the purposes of this document, the terms and definitions given in OPC 10000-1, OPC 10000-3, OPC 10000-4, OPC 10000-5, OPC 10000-7, OPC 10000-100, OPC 40001-1, as well as the following apply.

Note that OPC UA terms and terms defined in this specification are italicized in the specification.

Piping and all Components between at least two distinct points, the inputs and outputs of the Airnet, in a Compressed Air System.

Note 1 to entry: A Component can be connected to multiple Airnets.

Note 2 to entry: Airnets may touch or overlap each other.

Note 3 to entry: For examples on how Airnets can be used in the context of this specification see chapter 6.

Identifiable and browsable element in a Compressed Air System.

Note 1 to entry: CASParts defined in this specification are: Airnet, all Components, Main Control System.

CASPart that serves a particular purpose in compressed air generation, treatment, measurement, or storage.

Note 1 to entry: Components defined in this specification are: Charging System, Compressor, Condensate Drain, Condensate Separator, Converter, Cooling System, Dryer, Filter, Heat Recovery System, Receiver, Sensor.

Note 2 to entry: A Component may be connected to no, one, or more than one Airnet.

System that generates compressed air, consists of Components and at least one Airnet, and is commonly equipped with one Main Control System.

Specific type of a Component and value of the ComponentClass Variable of an instance of the FunctionalGroup Design of a Component.

EXAMPLE 1The compressor C1 is of the ComponentClass Axial turbo compressor.

EXAMPLE 2The filter F1 is of the ComponentClass Activated carbon filter.

Connection point of a Compressed Air System to subsequent machines or systems.

Note 1 to entry: Usually the Customer Distribution Point is located at one of the outlets of an Airnet.

Note 2 to entry: The Customer Distribution Point provides Variables and/or Objects which describe the conditions of the compressed air.

Specific class of a CASPart and value of the DeviceClass Property of an instance of the FunctionalGroup Identification of a CASPart.

Note 1 to entry: Available DeviceClasses for CASPart of this specification are listed in Table 9.

EXAMPLE 1The compressor C1 is of the DeviceClass Compressor.

EXAMPLE 2The filter F1 is of the DeviceClass Filter.

Instance of the FunctionalGroupType or one of its subtypes.

Note 1 to entry: In this specification, FunctionalGroup usually refers to an instance of a Compressed Air System specific ObjectType like OperationalType, AnalysesType, or DesignType.

EXAMPLE 1The compressor C1 has the FunctionalGroups Identification, Design, and Operational.

BrowseName of instances of the OptionalPlaceholder Object <ComponentsGroup> of instances of the ObjectType ComponentsGroupType.

Note 1 to entry: Available GroupNames for part groups of this specification are listed in Table 9.

EXAMPLE 1The Object for organizing all compressors in this Compressed Air System uses the GroupName Compressors.

EXAMPLE 2The Object for organizing all Airnets in this Compressed Air System uses the GroupName Airnets.

A Component is Integrated if the Main Control System has control over the generation or treatment of compressed air.

Note 1 to entry: A compressor is Integrated if the Main Control System has control over the loaded state.

Note 2 to entry: The Main Control System can switch a Component between the two states Integrated and Isolated.

A Component is Isolated if the Main Control System has no control over the generation or treatment of compressed air.

Note 1 to entry: A Component is Isolated if the Main Control System does not control the loaded state.

Note 2 to entry: The Main Control System can switch a Component between the two states Integrated and Isolated.

CASPart that controls all Components and Airnets simultaneously, represents the Compressed Air System, and serves for communication between the Components and higher-level systems.

The actual main function of Components is not specified in this specification. The following examples of Main Functions do not imply the actual function of the referenced Component.

EXAMPLE 1Charging system: to keep pressure upstream above a set minimum pressure or within a set pressure range

EXAMPLE 2Compressor: to deliver compressed air into the piping with an expected volume flow and at an expected pressure

EXAMPLE 3Condensate drain: to remove condensate from the compressed air piping or a condensate storage to outside the pressure system

EXAMPLE 4Condensate separator: to separate the hydrocarbon contents from the condensate to create a clean condensate that can easily be disposed of

EXAMPLE 5Converter: to eliminates hydrocarbons from the compressed air stream to create class 1 (and better) oil free air

EXAMPLE 6Cooling system: to reduce the compressed air temperature to a desired level

EXAMPLE 7Dryer: to remove moisture from compressed air and dry compressed air to a pressure dew point below the required value

EXAMPLE 8Filter: to remove particles and aerosols from the compressed air flow

EXAMPLE 9Heat recovery system: Main function: to heat up a material or substance flow by using the heat generated by the compressed air system

EXAMPLE 10Receiver: to store compressed air and provide a buffer

EXAMPLE 11Sensor: to measure specific parameters in the compressed air system and provide the data

A Variable representing physical measurements performed by a sensor, or calculations performed by a CASPart or the Main Control System to simulate a physical measurement.

Note 1 to entry: A physical quantity may be measured by an external sensor but is assigned to a specific CASPart.

Note 2 to entry: The measuring sensor may be integrated into the CASPart.

Note 3 to entry: A calculation performed on the Main Control System which is used by a Component shall be assigned to that Component.

EXAMPLE 1A temperature Quantity is measured by an internal sensor of a compressor at its outlet.

EXAMPLE 2A pressure Quantity is measured by an external sensor at the inlet and outlet of a filter.

EXAMPLE 3The isentropic efficiency of a compressor is a Quantity which is calculated by the Main Control System but assigned to the compressor.

The actual requirements of an Airnet are not specified in this specification. The following examples of Requirements do not imply the actual requirements of an Airnet.

EXAMPLE 1The Airnet pressure shall be within range.

EXAMPLE 2The dew point shall be within range.

EXAMPLE 3The volume flow rate shall be within range.

A compressor is Unavailable if it cannot be Integrated and controlled by the Main Control System.

Note 1 to entry: The Main Control System cannot switch a compressor from Unavailable to any other state.

EXAMPLE 1A compressor in an error state may be Unavailable.

CASCompressed Air System

HOCHeat of Compression Dryer

KPIkey performance indicator

MCSMain Control System

VSDVariable Speed Drive

Node definitions are specified using tables (see Table 2 ).

Attributes are defined by providing the Attribute name and a value, or a description of the value.

References are defined by providing the ReferenceType name, the BrowseName of the TargetNode and its NodeClass.

• If the TargetNode is a component of the Node being defined in the table the Attributes of the composed Node are defined in the same row of the table.
• The DataType is only specified for Variables; “[<number>]” indicates a single-dimensional array, for multi-dimensional arrays the expression is repeated for each dimension (e.g. [2][3] for a two-dimensional array). For all arrays the ArrayDimensions is set as identified by <number> values. If no <number> is set, the corresponding dimension is set to 0, indicating an unknown size. If no number is provided at all the ArrayDimensions can be omitted. If no brackets are provided, it identifies a scalar DataType and the ValueRank is set to the corresponding value (see OPC 10000-3). In addition, ArrayDimensions is set to null or is omitted. If it can be Any or ScalarOrOneDimension, the value is put into “{<value>}”, so either “{Any}” or “{ScalarOrOneDimension}” and the ValueRank is set to the corresponding value (see OPC 10000-3) and the ArrayDimensions is set to null or is omitted. Examples are given in Table 1 .

Table 1 – Examples of DataTypes

Notation	DataType	ValueRank	ArrayDimensions	Description
0:Int32	0:Int32	-1	omitted or null	A scalar Int32.
0:Int32[]	0:Int32	1	omitted or {0}	Single-dimensional array of Int32 with an unknown size.
0:Int32[][]	0:Int32	2	omitted or {0,0}	Two-dimensional array of Int32 with unknown sizes for both dimensions.
0:Int32[3][]	0:Int32	2	{3,0}	Two-dimensional array of Int32 with a size of 3 for the first dimension and an unknown size for the second dimension.
0:Int32[5][3]	0:Int32	2	{5,3}	Two-dimensional array of Int32 with a size of 5 for the first dimension and a size of 3 for the second dimension.
0:Int32{Any}	0:Int32	-2	omitted or null	An Int32 where it is unknown if it is scalar or array with any number of dimensions.
0:Int32{ScalarOrOneDimension}	0:Int32	-3	omitted or null	An Int32 where it is either a single-dimensional array or a scalar.

• The TypeDefinition is specified for Objects and Variables.
• The TypeDefinition column specifies a symbolic name for a NodeId, i.e. the specified Node points with a HasTypeDefinition Reference to the corresponding Node.
• The ModellingRule of the referenced component is provided by specifying the symbolic name of the rule in the ModellingRule column. In the AddressSpace, the Node shall use a HasModellingRule Reference to point to the corresponding ModellingRule Object.

If the NodeId of a DataType is provided, the symbolic name of the Node representing the DataType shall be used.

Note that if a symbolic name of a different namespace is used, it is prefixed by the NamespaceIndex (see 3.4.2.2).

Nodes of all other NodeClasses cannot be defined in the same table; therefore only the used ReferenceType, their NodeClass and their BrowseName are specified. A reference to another part of this document points to their definition.

Table 2 illustrates the table. If no components are provided, the DataType, TypeDefinition and ModellingRule columns may be omitted and only a Comment column is introduced to point to the Node definition.

Table 2 – Type Definition Table

Attribute	Value
Attribute name	Attribute value. If it is an optional Attribute that is not set “--“ will be used.
References	NodeClass	BrowseName	DataType	TypeDefinition	Other
ReferenceType name	NodeClass of the TargetNode.	BrowseName of the target Node. If the Reference is to be instantiated by the server, then the value of the target Node’s BrowseName is “--“.	DataType of the referenced Node, only applicable for Variables.	TypeDefinition of the referenced Node, only applicable for Variables and Objects.	Additional characteristics of the TargetNode such as the ModellingRule or AccessLevel.
NOTE Notes referencing footnotes of the table content.

Components of Nodes can be complex that is containing components by themselves. The TypeDefinition, NodeClass and DataType can be derived from the type definitions, and the symbolic name can be created as defined in 3.4.3.1. Therefore, those containing components are not explicitly specified; they are implicitly specified by the type definitions.

The Other column defines additional characteristics of the Node. Examples of characteristics that can appear in this column are show in Table 3.

Table 3 – Examples of Other Characteristics

Name	Short Name	Description
0:Mandatory	M	The Node has the Mandatory ModellingRule.
0:Optional	O	The Node has the Optional ModellingRule.
0:MandatoryPlaceholder	MP	The Node has the MandatoryPlaceholder ModellingRule.
0:OptionalPlaceholder	OP	The Node has the OptionalPlaceholder ModellingRule.
ReadOnly	RO	The Node AccessLevel has the CurrentRead bit set but not the CurrentWrite bit.
ReadWrite	RW	The Node AccessLevel has the CurrentRead and CurrentWrite bits set.
WriteOnly	WO	The Node AccessLevel has the CurrentWrite bit set but not the CurrentRead bit.

If multiple characteristics are defined they are separated by commas. The name or the short name may be used.

The NodeIds of all Nodes described in this standard are only symbolic names. Annex A defines the actual NodeIds.

The symbolic name of each Node defined in this document is its BrowseName, or, when it is part of another Node, the BrowseName of the other Node, a “.”, and the BrowseName of itself. In this case “part of” means that the whole has a HasProperty or HasComponent Reference to its part. Since all Nodes not being part of another Node have a unique name in this document, the symbolic name is unique.

The NamespaceUri for all NodeIds defined in this document is defined in Annex A. The NamespaceIndex for this NamespaceUri is vendor-specific and depends on the position of the NamespaceUri in the server namespace table.

Note that this document not only defines concrete Nodes, but also requires that some Nodes shall be generated, for example one for each Session running on the Server. The NodeIds of those Nodes are Server-specific, including the namespace. But the NamespaceIndex of those Nodes cannot be the NamespaceIndex used for the Nodes defined in this document, because they are not defined by this document but generated by the Server.

The text part of the BrowseNames for all Nodes defined in this document is specified in the tables defining the Nodes. The NamespaceUri for all BrowseNames defined in this document is defined in Annex A.

If the BrowseName is not defined by this document, a namespace index prefix like ‘0:EngineeringUnits’ or ‘2:DeviceRevision’ is added to the BrowseName. This is typically necessary if a Property of another specification is overwritten or used in the OPC UA types defined in this document. Table 184 provides a list of namespaces and their indexes as used in this document.

The Attributes of Nodes, their DataTypes and descriptions are defined in OPC 10000-3. Attributes not marked as optional are mandatory and shall be provided by a Server. The following tables define if the Attribute value is defined by this specification or if it is server-specific.

For all Nodes specified in this specification, the Attributes named in Table 4 shall be set as specified in the table.

Table 4 – Common Node Attributes

Attribute	Value
DisplayName	The DisplayName is a LocalizedText. Each server shall provide the DisplayName identical to the BrowseName of the Node for the LocaleId “en”. Whether the server provides translated names for other LocaleIds is server-specific.
Description	Optionally a server-specific description is provided.
NodeClass	Shall reflect the NodeClass of the Node.
NodeId	The NodeId is described by BrowseNames as defined in 3.4.2.1.
WriteMask	Optionally the WriteMask Attribute can be provided. If the WriteMask Attribute is provided, it shall set all non-server-specific Attributes to not writable. For example, the Description Attribute may be set to writable since a Server may provide a server-specific description for the Node. The NodeId shall not be writable, because it is defined for each Node in this specification.
UserWriteMask	Optionally the UserWriteMask Attribute can be provided. The same rules as for the WriteMask Attribute apply.
RolePermissions	Optionally server-specific role permissions can be provided.
UserRolePermissions	Optionally the role permissions of the current Session can be provided. The value is server-specific and depend on the RolePermissions Attribute (if provided) and the current Session.
AccessRestrictions	Optionally server-specific access restrictions can be provided.

For all Objects specified in this specification, the Attributes named in Table 5 shall be set as specified in the table. The definitions for the Attributes can be found in OPC 10000-3.

Table 5 – Common Object Attributes

Attribute	Value
EventNotifier	Whether the Node can be used to subscribe to Events or not is server-specific.

For all Variables specified in this specification, the Attributes named in Table 6 shall be set as specified in the table. The definitions for the Attributes can be found in OPC 10000-3.

Table 6 – Common Variable Attributes

Attribute	Value
MinimumSamplingInterval	Optionally, a server-specific minimum sampling interval is provided.
AccessLevel	The access level for Variables used for type definitions is server-specific, for all other Variables defined in this specification, the access level shall allow reading; other settings are server-specific.
UserAccessLevel	The value for the UserAccessLevel Attribute is server-specific. It is assumed that all Variables can be accessed by at least one user.
Value	For Variables used as InstanceDeclarations, the value is server-specific; otherwise it shall represent the value described in the text.
ArrayDimensions	If the ValueRank does not identify an array of a specific dimension (i.e. ValueRank <= 0) the ArrayDimensions can either be set to null or the Attribute is missing. This behavior is server-specific. If the ValueRank specifies an array of a specific dimension (i.e. ValueRank > 0) then the ArrayDimensions Attribute shall be specified in the table defining the Variable.
Historizing	The value for the Historizing Attribute is server-specific.
AccessLevelEx	If the AccessLevelEx Attribute is provided, it shall have the bits 8, 9, and 10 set to 0, meaning that read and write operations on an individual Variable are atomic, and arrays can be partly written.

For all VariableTypes specified in this specification, the Attributes named in Table 7 shall be set as specified in the table. The definitions for the Attributes can be found in OPC 10000-3.

Table 7 – Common VariableType Attributes

Attributes	Value
Value	Optionally a server-specific default value can be provided.
ArrayDimensions	If the ValueRank does not identify an array of a specific dimension (i.e. ValueRank <= 0) the ArrayDimensions can either be set to null or the Attribute is missing. This behavior is server-specific. If the ValueRank specifies an array of a specific dimension (i.e. ValueRank > 0) then the ArrayDimensions Attribute shall be specified in the table defining the VariableType.

For all Methods specified in this specification, the Attributes named in Table 8 shall be set as specified in the table. The definitions for the Attributes can be found in OPC 10000-3.

Table 8 – Common Method Attributes

Attributes	Value
Executable	All Methods defined in this specification shall be executable (Executable Attribute set to “True”), unless it is defined differently in the Method definition.
UserExecutable	The value of the UserExecutable Attribute is server-specific. It is assumed that all Methods can be executed by at least one user.